1. Field of Invention
The present invention relates generally to a vehicle-mounted alternator, and more particularly, to a vehicle-mounted alternator that has reduced noise.
2. Description of Related Art
In a belt-driven alternator for vehicles, there has been a growing demand for increasing the current output of the alternator in order to meet increased various electric loads adopted for improving driving safety and comfort in a vehicle. As a result, the inertial force of the rotor has been increased with the increased size of the alternator. There is, however, such a problem that since the inertial torque of the rotor is transmitted to the crankshaft during engine deceleration when the vehicle is running, early belt failure and noise caused by belt slippage occurs. To cope with this problem, the use of a pulley with a built-in one-way clutch (hereinafter referred to as the clutch pulley) has been known as disclosed in JP-A No. Hei 7-72585. According to the clutch pulley, the rotational power is transmitted to the alternator when the engine rpm increases, and to the contrary, no inertial torque of the alternator is transmitted to the driving belt when the engine rpms decrease.
On the other hand, for the purpose of environmental protection by reducing exhaust emissions and also as a link of enhancing fuel economy, there has been carried out an effort to stop engines when temporarily stopping a vehicle, particularly a shuttle bus for city driving, at an intersection according to a traffic signal. Also in the case of passenger cars and trucks in general, the adoption of an idle stop system for automatically stopping the engine at an intersection is being contemplated.
When the clutch pulley disclosed in JP-A No. Hei 7-72585 is adopted in the alternator for vehicles, the rotor of the alternator runs idle with its own inertial force for some time even after the engine is decelerated to a stop and disconnected from the alternator rotor by the clutch pulley. During this period, only the rotor of the alternator continues to rotate within the engine compartment. Besides, the rotor rotates with the cooling fan, and generally the rotor of the alternator for vehicles has a Randale-type magnetic pole having a fan effect. When the engine is stopped, engine noise does not occur. So, only such noises like a sound of rotation of the rotor and wind noise made by the cooling fan and the magnetic poles in the engine compartment will be audible and grating to the ear. Futhermore, recent alternators for vehicles are provided with many air vents in the frame for improving cooling performance, and therefore the noise produced by the rotation of the rotor is difficult to reduce and cannot be shielded from the alternator, thus becoming more and more grating to the ear.
Futhermore, if the engine is frequently stopped in urban areas because of the adoption of the idle stop system, noise from the vehicle-mounted alternator will be heard every time the engine is stopped, which will further disturb any listeners, thereby substantially degrading the quality of the vehicle which is required to be pleasant for human senses.
In view of the above described problem, it is an object of this invention to provide an alternator for vehicles which operates calmly with improved reliability of the driving belt and enhanced fuel economy to improve environmental conditions. More particularly, it is another object of this invention to decrease noise from the alternator for vehicles that are equipped with the idle stop system, while preventing early breakage or slippage noise of the belt by the clutch pulley.
To accomplish the above described object, a first aspect of this invention provides a pulley driven by a belt by the rotation of an engine crankshaft, a rotor connected to the pulley, a stator located opposite the rotor, a ventilating means rotating in one body with the rotor, and a frame with a plurality of cooling air vents as the ventilating means and holding the rotor and the stator. The pulley is mounted on a rotating shaft of the rotor through a one-way clutch which transmits driving power to the rotor during acceleration of rotaional speed of the crankshaft and does not transmit the driving power to the rotor during deceleration of rotational speed of the crankshaft. The rotor has a plurality of magnetic poles surrounding a field coil, and an alternator control mechanism which supplies a predetermined exciting current to the field coil upon sensing an engine stop condition. The rotating period of the alternator rotor during engine stop can be reduced while preventing early breakage and slippage noise of the belt during ordinary vehicle driving. Therefore it is possible to reduce noise from the alternator.
In another aspect, the alternator control mechanism previously stated has an engine stop signal input section, and sets the alternator voltage at a high value upon receiving the signal. It is therefore possible to reduce the idling time of the rotor by supplying the exciting current to the field coil when the engine is stopped.
In another aspect, the alternator for vehicles has a pulley driven by a belt by the rotation of an engine crankshaft, a rotor connected to the pulley, a stator located opposite to the rotor, a ventilating means rotating with the rotor, and a frame with a plurality of colling air vents as the ventilating means and a holding apparatus of the rotor and the stator.
The pulley is mounted on a rotating shaft of the rotor through a one-way clutch which transmits driving power to the rotor during acceleration of rotational speed of the crankshaft and does not transmit the driving power to the rotor during deceleration of rotational speed of the crankshaft.
The rotor has a plurality of magnetic poles surrounding a field coil, and an alternator control mechanism which controls an exciting current supplied to the field coil. The alternator for vehicles is characterized in that the alternator control mechanism has a signal input section, which receives a signal from the engine control mechanism to stop engine rotation upon sensing a vehicle stop, and supplies a predetermined exciting current to the field coil after receiving an engine stop signal from the engine control mechanism.
It is therefore possible to reduce the rotating period of the alternator rotor during engine stoppage and preventing early breakage and slippage noise of the belt in ordinary vehicle driving. Particularly, in the idle stop system, it is possible to decrease noise from the alternator.
In another aspect, the alternator control mechanism sets the alternator output voltage at a high value upon receiving an engine stop instruction signal. It is, therefore, possible to reduce the rotating period of the alternator rotor by supplying the exciting current to the field coil when the engine stops.
In another aspect, the invention has an alternator control mechanism which will stop the exciting current upon sensing a stop of the rotor. Thus it is possible to reduce the rotating period of the alternator rotor and prevent thermal deterioration by maintaining supply of the field current when the rotor is stopped.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.